1 /* 2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/javaClasses.hpp" 27 #include "classfile/stringTable.hpp" 28 #include "classfile/systemDictionary.hpp" 29 #include "classfile/vmSymbols.hpp" 30 #include "code/codeCache.hpp" 31 #include "code/icBuffer.hpp" 32 #include "gc_implementation/shared/gcHeapSummary.hpp" 33 #include "gc_implementation/shared/gcTimer.hpp" 34 #include "gc_implementation/shared/gcTrace.hpp" 35 #include "gc_implementation/shared/gcTraceTime.hpp" 36 #include "gc_interface/collectedHeap.inline.hpp" 37 #include "memory/genCollectedHeap.hpp" 38 #include "memory/genMarkSweep.hpp" 39 #include "memory/genOopClosures.inline.hpp" 40 #include "memory/generation.inline.hpp" 41 #include "memory/modRefBarrierSet.hpp" 42 #include "memory/referencePolicy.hpp" 43 #include "memory/space.hpp" 44 #include "oops/instanceRefKlass.hpp" 45 #include "oops/oop.inline.hpp" 46 #include "prims/jvmtiExport.hpp" 47 #include "runtime/fprofiler.hpp" 48 #include "runtime/handles.inline.hpp" 49 #include "runtime/synchronizer.hpp" 50 #include "runtime/thread.inline.hpp" 51 #include "runtime/vmThread.hpp" 52 #include "utilities/copy.hpp" 53 #include "utilities/events.hpp" 54 55 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, bool clear_all_softrefs) { 56 guarantee(level == 1, "We always collect both old and young."); 57 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 58 59 GenCollectedHeap* gch = GenCollectedHeap::heap(); 60 #ifdef ASSERT 61 if (gch->collector_policy()->should_clear_all_soft_refs()) { 62 assert(clear_all_softrefs, "Policy should have been checked earlier"); 63 } 64 #endif 65 66 // hook up weak ref data so it can be used during Mark-Sweep 67 assert(ref_processor() == NULL, "no stomping"); 68 assert(rp != NULL, "should be non-NULL"); 69 _ref_processor = rp; 70 rp->setup_policy(clear_all_softrefs); 71 72 GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer->gc_id()); 73 74 gch->trace_heap_before_gc(_gc_tracer); 75 76 // When collecting the permanent generation Method*s may be moving, 77 // so we either have to flush all bcp data or convert it into bci. 78 CodeCache::gc_prologue(); 79 80 // Increment the invocation count 81 _total_invocations++; 82 83 // Capture heap size before collection for printing. 84 size_t gch_prev_used = gch->used(); 85 86 // Capture used regions for each generation that will be 87 // subject to collection, so that card table adjustments can 88 // be made intelligently (see clear / invalidate further below). 89 gch->save_used_regions(level); 90 91 allocate_stacks(); 92 93 mark_sweep_phase1(level, clear_all_softrefs); 94 95 mark_sweep_phase2(); 96 97 // Don't add any more derived pointers during phase3 98 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity")); 99 COMPILER2_PRESENT(DerivedPointerTable::set_active(false)); 100 101 mark_sweep_phase3(level); 102 103 mark_sweep_phase4(); 104 105 restore_marks(); 106 107 // Set saved marks for allocation profiler (and other things? -- dld) 108 // (Should this be in general part?) 109 gch->save_marks(); 110 111 deallocate_stacks(); 112 113 // If compaction completely evacuated all generations younger than this 114 // one, then we can clear the card table. Otherwise, we must invalidate 115 // it (consider all cards dirty). In the future, we might consider doing 116 // compaction within generations only, and doing card-table sliding. 117 bool all_empty = true; 118 if (level == 1) { 119 all_empty = gch->young_gen()->used() == 0; 120 } 121 122 GenRemSet* rs = gch->rem_set(); 123 assert(level == 1, "Code will break if this isn't true."); 124 Generation* old_gen = gch->old_gen(); 125 // Clear/invalidate below make use of the "prev_used_regions" saved earlier. 126 if (all_empty) { 127 // We've evacuated all generations below us. 128 rs->clear_into_younger(old_gen); 129 } else { 130 // Invalidate the cards corresponding to the currently used 131 // region and clear those corresponding to the evacuated region. 132 rs->invalidate_or_clear(old_gen); 133 } 134 135 CodeCache::gc_epilogue(); 136 JvmtiExport::gc_epilogue(); 137 138 if (PrintGC && !PrintGCDetails) { 139 gch->print_heap_change(gch_prev_used); 140 } 141 142 // refs processing: clean slate 143 _ref_processor = NULL; 144 145 // Update heap occupancy information which is used as 146 // input to soft ref clearing policy at the next gc. 147 Universe::update_heap_info_at_gc(); 148 149 // Update time of last gc for all generations we collected 150 // (which currently is all the generations in the heap). 151 // We need to use a monotonically non-decreasing time in ms 152 // or we will see time-warp warnings and os::javaTimeMillis() 153 // does not guarantee monotonicity. 154 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 155 gch->update_time_of_last_gc(now); 156 157 gch->trace_heap_after_gc(_gc_tracer); 158 } 159 160 void GenMarkSweep::allocate_stacks() { 161 GenCollectedHeap* gch = GenCollectedHeap::heap(); 162 // Scratch request on behalf of oldest generation; will do no 163 // allocation. 164 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0); 165 166 // $$$ To cut a corner, we'll only use the first scratch block, and then 167 // revert to malloc. 168 if (scratch != NULL) { 169 _preserved_count_max = 170 scratch->num_words * HeapWordSize / sizeof(PreservedMark); 171 } else { 172 _preserved_count_max = 0; 173 } 174 175 _preserved_marks = (PreservedMark*)scratch; 176 _preserved_count = 0; 177 } 178 179 180 void GenMarkSweep::deallocate_stacks() { 181 if (!UseG1GC) { 182 GenCollectedHeap* gch = GenCollectedHeap::heap(); 183 gch->release_scratch(); 184 } 185 186 _preserved_mark_stack.clear(true); 187 _preserved_oop_stack.clear(true); 188 _marking_stack.clear(); 189 _objarray_stack.clear(true); 190 } 191 192 void GenMarkSweep::mark_sweep_phase1(int level, 193 bool clear_all_softrefs) { 194 // Recursively traverse all live objects and mark them 195 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 196 trace(" 1"); 197 198 GenCollectedHeap* gch = GenCollectedHeap::heap(); 199 200 // Because follow_root_closure is created statically, cannot 201 // use OopsInGenClosure constructor which takes a generation, 202 // as the Universe has not been created when the static constructors 203 // are run. 204 assert(level == 1, "We don't use mark-sweep on young generations"); 205 follow_root_closure.set_orig_generation(gch->old_gen()); 206 207 // Need new claim bits before marking starts. 208 ClassLoaderDataGraph::clear_claimed_marks(); 209 210 gch->gen_process_roots(level, 211 false, // Younger gens are not roots. 212 true, // activate StrongRootsScope 213 SharedHeap::SO_None, 214 GenCollectedHeap::StrongRootsOnly, 215 &follow_root_closure, 216 &follow_root_closure, 217 &follow_cld_closure); 218 219 // Process reference objects found during marking 220 { 221 ref_processor()->setup_policy(clear_all_softrefs); 222 const ReferenceProcessorStats& stats = 223 ref_processor()->process_discovered_references( 224 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer, _gc_tracer->gc_id()); 225 gc_tracer()->report_gc_reference_stats(stats); 226 } 227 228 // This is the point where the entire marking should have completed. 229 assert(_marking_stack.is_empty(), "Marking should have completed"); 230 231 // Unload classes and purge the SystemDictionary. 232 bool purged_class = SystemDictionary::do_unloading(&is_alive); 233 234 // Unload nmethods. 235 CodeCache::do_unloading(&is_alive, purged_class); 236 237 // Prune dead klasses from subklass/sibling/implementor lists. 238 Klass::clean_weak_klass_links(&is_alive); 239 240 // Delete entries for dead interned strings. 241 StringTable::unlink(&is_alive); 242 243 // Clean up unreferenced symbols in symbol table. 244 SymbolTable::unlink(); 245 246 gc_tracer()->report_object_count_after_gc(&is_alive); 247 } 248 249 250 void GenMarkSweep::mark_sweep_phase2() { 251 // Now all live objects are marked, compute the new object addresses. 252 253 // It is imperative that we traverse perm_gen LAST. If dead space is 254 // allowed a range of dead object may get overwritten by a dead int 255 // array. If perm_gen is not traversed last a Klass* may get 256 // overwritten. This is fine since it is dead, but if the class has dead 257 // instances we have to skip them, and in order to find their size we 258 // need the Klass*! 259 // 260 // It is not required that we traverse spaces in the same order in 261 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 262 // tracking expects us to do so. See comment under phase4. 263 264 GenCollectedHeap* gch = GenCollectedHeap::heap(); 265 266 GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 267 trace("2"); 268 269 gch->prepare_for_compaction(); 270 } 271 272 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure { 273 public: 274 void do_generation(Generation* gen) { 275 gen->adjust_pointers(); 276 } 277 }; 278 279 void GenMarkSweep::mark_sweep_phase3(int level) { 280 GenCollectedHeap* gch = GenCollectedHeap::heap(); 281 282 // Adjust the pointers to reflect the new locations 283 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 284 trace("3"); 285 286 // Need new claim bits for the pointer adjustment tracing. 287 ClassLoaderDataGraph::clear_claimed_marks(); 288 289 // Because the closure below is created statically, we cannot 290 // use OopsInGenClosure constructor which takes a generation, 291 // as the Universe has not been created when the static constructors 292 // are run. 293 assert(level == 1, "We don't use mark-sweep on young generations."); 294 adjust_pointer_closure.set_orig_generation(gch->old_gen()); 295 296 gch->gen_process_roots(level, 297 false, // Younger gens are not roots. 298 true, // activate StrongRootsScope 299 SharedHeap::SO_AllCodeCache, 300 GenCollectedHeap::StrongAndWeakRoots, 301 &adjust_pointer_closure, 302 &adjust_pointer_closure, 303 &adjust_cld_closure); 304 305 gch->gen_process_weak_roots(&adjust_pointer_closure); 306 307 adjust_marks(); 308 GenAdjustPointersClosure blk; 309 gch->generation_iterate(&blk, true); 310 } 311 312 class GenCompactClosure: public GenCollectedHeap::GenClosure { 313 public: 314 void do_generation(Generation* gen) { 315 gen->compact(); 316 } 317 }; 318 319 void GenMarkSweep::mark_sweep_phase4() { 320 // All pointers are now adjusted, move objects accordingly 321 322 // It is imperative that we traverse perm_gen first in phase4. All 323 // classes must be allocated earlier than their instances, and traversing 324 // perm_gen first makes sure that all Klass*s have moved to their new 325 // location before any instance does a dispatch through it's klass! 326 327 // The ValidateMarkSweep live oops tracking expects us to traverse spaces 328 // in the same order in phase2, phase3 and phase4. We don't quite do that 329 // here (perm_gen first rather than last), so we tell the validate code 330 // to use a higher index (saved from phase2) when verifying perm_gen. 331 GenCollectedHeap* gch = GenCollectedHeap::heap(); 332 333 GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 334 trace("4"); 335 336 GenCompactClosure blk; 337 gch->generation_iterate(&blk, true); 338 }